Anti-icing jet fuel composition containing a hexaalkyl phosphoric triamide



Jan. 26, 1965 J. J. BIALY ETAL 3,167,411

ANTI-ICING JET FUEL COMPOSITION CONTAINING A HEXAALKYL PHOSPHORICTRIAMIDE Filed Feb. 28, 1962 27 .fm-@i2 1 22 i I f4 l United StatesPatent C) ING A HEXAALKYL PHSPHRC TRIAMIDE Jerzy J. Bialy, Beacon, andGeorge W. Eckert, Wap- This invention relates to a novel fuelcomposition. More particularly, the invention rel-ates to turbine or jetfuels having outstanding anti-icing properties. This improvement isbased on the effect of an anti-icing additive consisting of a polyalkylphosphoric triarnide.

Reliability of the fuel supply under extremely severe operatingconditions is a matter of paramount importance in the operation ofturbine or jet engine aircraft. It is also essential that the fuelsupply be absolutely free of any suspended solid particles in order notto block or impair the operation of the fuel atomizer and other finecomponents in the jet engine. The provision of uncontaminated fuel freeof soli-d particles to the engine is assured by passing the fuel throughexceedingly fine filters yin order to screenout any` contained solidparticles.

let fuels always contain minor amounts of water dis- Asolved in the fuelitself. When proper care has not been taken in the handling of the fuel,water in excess of the hamount dissolved in the fuel will often bepresent. Jet

engine aircraft frequently encounter extremely low-temperature operatingconditions which cause the water in the fuel to form ice, generally inthe form of small crystals. These ice crystals are caught by the fuelfilter initially restricting and finally preventing passage of the fueltherethrough resulting in engine failure from the lack of fuel. A fuelcomposition has now been discovered which 'inhibits or prevents theformation of ice from the water cent of apolyaikyl phosphoric triamide.Polyalkyl phosphoric triamides are represented by the formula:

R-N-iL-N-R ff if N-R' t in which R and R each represent alkyl radicalshaving from l to 4 carbon atoms.

The preferred polyalkyl phosphoric triamide anti-icing additives of theinvention are the hexaalkyl phosphoric triamides, such as hexamethylphosphoric triamide, hexaethyl phosphoric triarnide, hexabutylphosphoric triamide, hexapropyl phosphoric triamide and the like. Mixedliexaalkyl phosphoric triamides are also effective as the anti-icingadditive. The preferred additive of this invention is hexarnethylphosphoric triamide.

.The anti-icing additive of this invention is employed in turbine or jetengine fuel compositions. The fuels are made up of straight run orcracked hydrocarbon components in the gasoline and kerosene boilingranges, i.e., boiling from about 100 to about 600 F. Commercial JP-4type jet fuel, which consists of about 65 percent gasoline and 35percent middle distillate, is typical ofthe fuels improved by theanti-icing additive of the invention.

ICC

The jet fuel of the invention is conveniently prepared by mixing thebase fuel with the polyalkyl phosphoric triamide. As noted above, thejet fuel will generally contain from about 0.02 to 0.35 weight percentof the additive. The preferred range of proportions for the additive,however, are from about 0.05 to 0.20 weight percent.

An important feature of this invention is that the outstandinganti-icing properties imparted to thefuel are obtained with relativelysmall amounts of the additive. Whereas heretofore, jet fuel anti-icingadditives have been proposed in amounts of 0.5 to l percent or more, thepresent additive gives the desired properties with a very small amountof additive. For most purposes, effective anti-icing is obtained atabout 0.10 weight percent of the additive.

The single figure is a schematic diagram of a test system fordetermining the pumpability temperature of fuels at low temperatures.

The temperature at which the iiow rate of the fuel can no longer bemaintained and/ or substantial pressure drop develops across the screenis defined as the pumpability temperature. i

Water-containing jet fuels of Ithe invention were tested for theirpurnpability properties at low temperature. Basically, the test involvedcirculating the fuel in a closed system containing a fine metal screenfilter while gradually reducing the temperature of the fuel. Sensitivetemperature and pressure devices placed on the inlet and outlet sides ofthe filter indicated the temperature at which a substantial pressuredrop was brought about by the formation of ice in the fuel.

Two criteria of additive performance were employed in the test; l

(l) Concentration of additive to yield 76 F. pumpability temperaturewith water-saturated fuel, and

(2) Concentration of additive to yield -45 F. pumpability temperaturewith water-saturated fuel to which 2 cc. per gallon of free water wasadded.

Referring now to FIGURE 1 showing a diagram of the low temperaturepumpability test system, 10 is a reservoir for the fuel sample. In thetest system employed, this reservoir hadl a capacity of four liters.Conduit 1l. connects the fuel reservoirwith a pump l2, and fiow meter i3which controls the rate of flow of the fuel. The test fuel is passedthrough conduit 14 into cooling coil 15 which is immersed in a lowtemperature cooling bath in vessel 16. The temperature of the coolingbath is registered by temperature means 17 and is controlled bycirculation from cooling liquid reservoir 18 and inlet and returncirculating conduits i9 and 20 respectively. The test fuel is passedthrough conduit 21 into filtering device 2?, which has a 200 mesh screenfilter 23 mounted therein for filtering the fuel. Conduit 24 is a returnline for the fuel to the sample reservoir. The filter device is equippedwith temperature indicating means 25 and 26 to indicate the temperatureon the inlet and outlet sides of the `filtering device respectively.This device is also equipped with a sensitive pressure means 27 to showthe pressure differential between that in the inlet conduit leading intothe filter and the pressure in the outlet conduit from the filter. Thepressure device is sensitive to a pressure differential of :t1 mm. ofmercury. Plugging of the filter caused by ice formation is indicated bya sharp pressure drop across the filter.

Cooling liquid reservoir 18 contains a Dry Ice-acetone mixture which iscirculated around the test cooling coil in vessel lo. Steady cooling ofthe test fuel is obtained by controlling the fiow of cooling liquidthrough conduits 19 and 20.

' The jet 'fuel employedV for ltes-ting 'the V'additive oftl'ie`vvinvention had the inspection tests listed in Table I below: j

Sat'urate's a The te'st procedure followed involves adding' 4 'lit`ersof the test fuelto the reservoirfvvhich is thereafter stoppered topreventfthe'fentrance ofwater from condensation f i during thecoolingpe'riod. The circulating pump'is started and airr is pur'ged'irom` the :nanometerlinesandiiilter ;screen housing via ventsprovidedfforthis purpose.V The -f uel flovv rateis adjusted to Y0.67giplm. '(gallons p erminutc). zAt the start of Kthe cooling cycle, 'theDry IceA compartment is filled with lDry Ice and the cold acetone'- Y(tial pressure continues tol increaseY at Vthisr temperatureV to thepoint'whereflow can nolonger'bemaintained, Athisis taken as thepumpability temperature: If vthe pressure i differential does notcontnue'to rise,'the temperature is A Jet fuelfhaving'theInspectiouTe'sts shownm Table I Y 'was tested for'V itsjpurnpabilitytemperatures in the =te'sty VYdevice and manner described.hereir xabove.The anti-icing Dry Ice solution is circulated-tothe' mainV bathr which 1Y' contains the cooling coils of the fuel test circuit. Dry'Ice isdropped 'intothej cooling bath initiallyv in quantities'sui-V cient tocoolzthe fuel rapidly to-ZO" F., then inV an amount to cool the Vfuelatthe krate of about 0.5 F. per rninute. The temperaturejof the coolingbathisgfurther controlled by controlling the 'flow of thecoolng liquid.Y Wherrthey first appreciable rise (5 to 10mm. in fscr'een pressuredifferential occurs, th e temperature prevail? ing at that timeismaintainedfor at least 5 minutes whilec` maintaining the fuel ow at' 0.67 g.p.m.` `Ifl the .differendecreased in 1 F. increments until alargeincrease in pressure differential occurs.'v Y- The purnpabilitytemperature fora'Water-saturated JP-4 fuel is 'usually between-f5 and 15l lF With l2 ml. `per gallon of Yfree water, thepumpability temperatureis gen-Y additive employedv consisted Aof hexarnethyl phosphoric`-.triamide. VThe tests Were conducted onl a fuel saturated-.with,waterand also on a fuel s aturatedfwithjand con# ftaining excess-Waterin vthe amount of= 2 Inl. of excess ivwiterper gallon of'fuel'.

At ahexamethyl phosphoric triamideconcentration of 0.1Weight',percerltLtlie fuel saturated with Water had a'pumpabilitytemperature of 76 F.

At .a f hexamethyl phosphoric triamide Vconcentration 1. AA-jetfuelrcomposition consisting essentially of (f1) Vgasoline'a'nd kerosenehydrocarbon fractions boiling fromv about 100- 60Qvdegree's P., saidhydrocarbon fractions being free of `alkyl lead antiknock compounds, and(2) an 4anti-icing'amount of a hexaalkyl phosphoric triamide lin Vwhichsaidalkylradicals have-from 1- tov4 carbon atoms.

l2.`A Vjet fuelcomposition "accordingtoclaim 1 containing'0.02 r to 0.35weight percent of said'heiaallylphos'- phorictriamide. .f-,i Y3. Ajet-fuel compositionaccording toclaim-l inwhich said triamide isVhexam'ethylphosphoric triamide.Y

l4. jet fuel composition according to claiml containing' fromiaboutOS to0.20weight percent'of said hexaalkyl `phosphoric' triamide.

5.- Ajetfuelcomposition ac cording'to'claim 4 in which rsaidvhexaalkylphosphoric triamide ishexamethyl phosvphorictriarnide.

Y 0.1 Weight percent;4V the fuel saturated'vvith water and containing2in1. of excess Water per gallon ofY fuel also had a .pumpabilityAtemperature'of -7 6 F.

1. A JET FUEL COMPOSITION CONSISTING ESSENTIALLY OF (1) GASOLINE ANDKEROSENE HYDROCARBON FRACTIONS BOILING FROM ABOUT 100-600 DEGREES F.,SAID HYDROCARBON FRACTIONS BEING FREE OF ALKYL LEAD ANTI-KNOCKCOMPOUNDS, AND (2) AN ANTI-ICING AMOUNT OF A HEXAALKYL PHOSPHORICTRIAMIDE IN WHICH SAID ALKYL RADICALS HAVE FROM 1 TO 4 CARBON ATOMS.